Mercury and methylmercury in riparian soil,sediments, mine-waste calcines,and moss from abandoned Hg mines in east Guizhou province,southwestern China

Concentrations of total Hg and methylmercury (MMHg) in riparian soil, mine-waste calcine, sediment, and moss samples collected from abandoned Hg mines in Wanshan district, Guizhou province, China, were measured to show regional dispersion of Hg-contamination. High total Hg and MMHg concentrations obtained in riparian soils from mined areas, ranged from 5.1 to 790 mg kg⁻¹ and 0.13 to 15 ng g⁻¹, respectively. However, total Hg and MMHg concentrations in the soils collected from control sites were significantly lower varying from 0.1 to 1.2 mg kg⁻¹ and 0.10 to 1.6 ng g⁻¹, respectively. Total Hg and MMHg concentrations in sediments varied from 90 to 930 mg kg⁻¹ and 3.0 to 20 ng g⁻¹, respectively. Total Hg concentrations in mine-waste calcines were highly elevated ranging from 5.7 to 4400 mg kg⁻¹, but MMHg concentrations were generally low ranging from 0.17 to 1.1 ng g⁻¹. Similar to the high Hg concentrations in soil and sediments, moss samples collected from rocks ranged from 1.0 to 95 mg kg⁻¹ in total Hg and from 0.21 to 20 ng g⁻¹ in MMHg. Elevated Hg concentrations in mosses suggest that atmospheric deposition might be an important pathway of Hg to the local terrestrial system. Moreover, the spatial distribution patterns of Hg contamination in the local environment suggest derivation from historic Hg mining sites in the Wanshan area.     

Gold mining related mercury contamination in Tongguan,Shaanxi Province,PR China

Elemental Hg–Au amalgamation mining practices are used widely in many developing countries resulting in significant Hg contamination of surrounding ecosystems. The authors examined for the first time Hg contamination in air, water, sediment, soil and crops in the Tongguan Au mining area, China, where elemental Hg has been used to extract Au for many years. Total gaseous Hg (TGM) concentrations in ambient air in the Tongguan area were significantly elevated compared to regional background concentrations. The average TGM concentrations in ambient air in a Au mill reached 18,000 ng m⁻³, which exceeds the maximum allowable occupational standard for TGM of 10,000 ng m⁻³ in China. Both total and methyl-Hg concentrations in stream water, stream sediment, and soil samples collected in the Tongguan area were elevated compared to methyl-Hg reported in artisanal Au mining areas in Suriname and the Amazon River basin. Total Hg concentrations in vegetable and wheat samples ranged from 42 to 640 μg kg⁻¹, all of which significantly exceed the Chinese guidance limit for vegetables (10 μg kg⁻¹) and foodstuffs other than fish (20 μg kg⁻¹). Fortunately, methyl-Hg was not significantly accumulated in the crops sampled in this study, where concentrations varied from 0.2 to 7.7 μg kg⁻¹.     

Mercury speciation in soils of the industrialised Thur River catchment (Alsace,France)

Methylmercury (MeHg) and total Hg (THg) concentrations in soil profiles were monitored in the Thur River basin (Alsace, France), where a chlor-alkali plant has been located in the city of Vieux-Thann since the 1930s. Three soil types were studied according to their characteristics and location in the catchment: industrial soil, grassland soil and alluvial soil. Contamination of MeHg and THg in soil was important in the vicinity of the plant, especially in industrial and alluvial soil. Concentrations of MeHg reached 27 ng g⁻¹ and 29,000 ng g⁻¹ for THg, exceeding the predictable no effect concentration. Significant ecotoxicological risk exists in this area and remedial actions on several soil types are suggested. In each type of soil, MeHg concentrations were highest in topsoil, which decreased with depth. Concentrations of MeHg were negatively correlated with soil organic matter and total S, particularly when MeHg concentrations exceeded 8 ng g⁻¹. Under these conditions, MeHg concentrations in soil seemed to be influenced by THg, soil organic matter and total S concentrations. It was found that high MeHg/THg ratios (near 2%) in soil were mainly related to the combined soil environmental conditions such as low THg concentrations, low organic C/N ratios (<11) and relatively low pH (5–5.5). Nevertheless, even when the MeHg/THg ratio was low (∼0.04%), MeHg and THg concentrations were elevated, up to 13 ng g⁻¹ and to 29,000 ng g⁻¹, respectively. Thus, both THg and MeHg concentrations should be taken into account to assess potential environmental risks of Hg.     

Weathering versus atmospheric contributions to mercury concentrations in French Guiana soils

This work focuses on two possible sources of Hg in tropical soils, (i) lithogenic Hg from in situ weathering of soil parental material, and (ii) exogenic Hg from natural long-term atmospheric inputs and anthropogenic input from past and present industrial activities. The concentration of lithogenic Hg [Hg]_lithogenic was based on comparison of measured Hg concentration with those of elements resistant to weathering such as Nb, U, Zn, Fe. Exogenic Hg was quantified by subtracting [Hg]_lithogenic from total Hg concentrations. This calculation was applied to 4 French Guiana soil profiles, 3 profiles on the same toposequence (ferralsol, acrisol, hydromorphic soil) and one acrisol close to a Au mine, where elemental Hg is used. In all profiles, [Hg]_lithogenic varied slightly and was always below 40 μg kg⁻¹, whereas [Hg]_exogenic varied considerably and reached 500 μg kg⁻¹. The highest [Hg]_exogenic was calculated for the upper horizon of the acrisol close to Au mining activity, but also in the ferralsol. Concentrations of Hg were insignificant in the compact alterite in acrisols. It was concluded that pedogenesis processes that affect the natural Hg supply, combined with anthropogenic sources, explain the Hg concentrations in these tropical soils.     

Selenium speciation,distribution, and transport in a river catchment affected by mercury mining and smelting in Wanshan,China

Selenium (Se) is an important co-existing elemental component of the mineral matrix of mercury (Hg) ore deposits. The hazards associated with Se contamination of the aquatic ecosystems in Hg mining areas; however, are often overlooked by environmental researchers due to a preoccupation with Hg. Selenium may also pose a long-term risk to the local ecosystem, and further complicate the situation as Se may also play an important antagonistic role against Hg. Furthermore, most studies on Se pollution have focused only on total Se, whereas the toxicity, bioavailability, and bioaccumulation of Se in aquatic ecosystems is primarily determined by its site-specific individual species. In this study, the concentrations of total Se, inorganic Se (tetravalent and hexavalent), and organic Se were determined in water samples collected from 41 typical sites selected in rivers, tributaries, and springs in Wanshan, China, where Hg and Se co-occur due to historic Hg mining and retorting activities. Se concentrations were observed to decrease with distance from mine-waste calcines, which indicated that mine-waste calcines may be significant sources of the elevated Se in the rivers, especially in downstream areas within 8 km from the mine-waste calcines. The concentration of total aqueous Se throughout the study area was highly variable (3.8 ± 6.0 μg L⁻¹) and on average was one order of magnitude greater than that in natural river systems worldwide (0.1–0.3 μg L⁻¹). The majority of the Se was hexavalent (3.1 ± 4.9 μg L⁻¹; 65%), followed by tetravalent (0.53 ± 0.86 μg L⁻¹; 15%) and organic forms (0.85 ± 1.5 μg L⁻¹; 20%), possibly due to the generally alkaline conditions. Se concentrations in some sampling sites exceeded certain recommended limit of values. However, the existing criteria for Se in aquatic system are mainly based on total Se and the recommended limit of values in different countries or organizations are inconsistent with one another. Therefore, the need to consider Se speciation rather than only total Se is highlighted for future studies.     

Mercury in European agricultural and grazing land soils

Agricultural (Ap, A_p-horizon, 0–20 cm) and grazing land soil samples (Gr, 0–10 cm) were collected from a large part of Europe (33 countries, 5.6 million km²) at an average density of 1 sample site/2500 km². The resulting more than 2 × 2000 soil samples were air dried, sieved to <2 mm and analysed for their Hg concentrations following an aqua regia extraction. Median concentrations for Hg are 0.030 mg/kg (range: <0.003–1.56 mg/kg) for the Ap samples and 0.035 mg/kg (range: <0.003–3.12 mg/kg) for the Gr samples. Only 5 Ap and 10 Gr samples returned Hg concentrations above 1 mg/kg. In the geochemical maps the continental-scale distribution of the element is clearly dominated by geology. Climate exerts an important influence. Mercury accumulates in those areas of northern Europe where a wet and cold climate favours the build-up of soil organic material. Typical anthropogenic sources like coal-fired power plants, waste incinerators, chlor-alkali plants, metal smelters and urban agglomerations are hardly visible at continental scales but can have a major impact at the local-scale.     

Mercury in sediments from gold and copper exploitation areas in the Camaquã River Basin,Southern Brazil

Mercury concentrations were determined in stream sediments from the Camaquã River Basin, located in the shield region of the state of Rio Grande do Sul, southern Brazil. The resulting geochemical data show that overbank floodplain deposits exhibit higher concentrations than sediments collected from the active channel bed. In addition, higher Hg concentrations were measured in the fine(<63 μm) sediment fraction of the samples. Total Hg concentrations in the fine fraction of active stream sediments from Lavras do Sul County, which have been influenced by past gold mining activities, have decreased during the last five years to values ≤142 ng g⁻¹. However, in a settling pond containing abandoned mine wastes, the Hg concentration of a bulk sample remained exceptionally high (5220 ng g⁻¹). Preliminary speciation results show that Hg⁰ is the predominant species in most of the samples. This was the form of Hg released by the gold amalgamation activities in the area, and appears to be relatively stable under the existing E_h and pH conditions.     

Mercury mobility in unsaturated gold mine tailings,Murray Brook mine,New Brunswick,Canada

Elevated concentrations of Hg are present (averaging 36 μg/g), mainly as cinnabar, in the Murray Brook Au deposit, located in northern New Brunswick, Canada. After the mined ore was subjected to CN leaching, the tailings were deposited in an unsaturated pile, and 10 a after mine closure an estimated 4.7 × 10³ kg of CN and 1.1 × 10⁴ kg of Hg remain in the pile. Elevated Hg concentrations have been measured in the groundwater (up to 11,500 μg/L) and surface water (up to 32 μg/L) down-gradient of the tailings. To investigate the controls on Hg mobility and leaching persistence, laboratory experiments were conducted using unsaturated columns filled with tailings. Within the first 0.2 pore volumes (PV) eluted, the concentrations of Hg and CN increased to peak concentrations of 12,900 μg Hg/L and 16 mg CN/L, respectively. In the subsequent 0.9 PV, concentrations decreased to approximately 1300 μg Hg/L and 2.8 mg CN/L. Thermodynamic calculations demonstrate that >99.8% of the mobilized Hg in the tailings pore water is in the form of Hg–CN complexes, indicating that Hg mobility to the surrounding aquatic environment is directly dependent on the rate of CN leaching. One-dimensional transport simulations suggest that leached CN can be partitioned into conservative (24%) and non-conservative (76%) fractions. Extrapolation of simulation results to the field scale suggests that CN, and by extension Hg, will continue to elute from the tailings for at least an additional 130 a.     

Mercury in water and biomass of microbial communities in hot springs of Yellowstone National Park,USA

Ultra-clean sampling methods and approaches typically used in pristine environments were applied to quantify concentrations of Hg species in water and microbial biomass from hot springs of Yellowstone National Park, features that are geologically enriched with Hg. Microbial populations of chemically-diverse hot springs were also characterized using modern methods in molecular biology as the initial step toward ongoing work linking Hg speciation with microbial processes. Molecular methods (amplification of environmental DNA using 16S rDNA primers, cloning, denatured gradient gel electrophoresis (DGGE) screening of clone libraries, and sequencing of representative clones) were used to examine the dominant members of microbial communities in hot springs. Total Hg (THg), monomethylated Hg (MeHg), pH, temperature, and other parameters influential to Hg speciation and microbial ecology are reported for hot springs water and associated microbial mats.Several hot springs indicate the presence of MeHg in microbial mats with concentrations ranging from 1 to 10 ng g⁻¹ (dry weight). Concentrations of THg in mats ranged from 4.9 to 120,000 ng g⁻¹ (dry weight). Combined data from surveys of geothermal water, lakes, and streams show that aqueous THg concentrations range from l to 600 ng L⁻¹. Species and concentrations of THg in mats and water vary significantly between hot springs, as do the microorganisms found at each site.     

Mercury in Baltic Sea sediments—Natural background and anthropogenic impact

In total 27 short and one long sediment core, and 278 surface sediment samples from the Baltic Sea were analyzed for mercury (Hg), and organic carbon contents. Thirteen short cores and the long core were dated by radionuclide methods (²¹⁰Pb, ¹³⁷Cs, AMS¹⁴C). The dataset allows discriminating between natural and human induced changes on the Hg levels in Baltic Sea sediments. Preindustrial Holocene background concentrations vary between 20 and 50 μg Hg per kg dry sediment and are positively correlated with organic carbon changes. Strong human induced pollution is recorded for the second half of the past century and caused high Hg concentrations of up to several hundred μg Hg per kg dry sediment even in Baltic Sea basins. Maximum concentrations are found at industrial and war waste dumping sites (local hot spots). An Hg concentration decreasing trend toward the present day is observed at most coring sites, a result of environmental measures undertaken during the last two decades. At sites where it is possible to calculate Hg fluxes, the natural accumulation rates vary between 2.1 and 5.4 μg Hg per m² per year. Anthropogenically sourced Hg accumulation rates vary in a wide range of 30 and 300 μg Hg per m² per year for the time span of maximum pollution. In areas characterized by discontinuous sedimentation only “inventories” of human sourced Hg expressed as the total amount of deposited Hg (above the natural background) per m² can be calculated. The inventories of the investigated cores vary in the range of 1 and 8 mg Hg per m². Additionally, influences of sediment dynamics on spatial distribution pattern of Hg concentrations in surface and subsurface sediments are discussed.     

Chlor-alkali industrial contamination and riverine transport of mercury: Distribution and partitioning of mercury between water,suspended matter,and bottom sediment of the Thur River,France

Total dissolved and total particulate Hg mass balances were estimated during one hydrological period (July 2001–June 2002) in the Thur River basin, which is heavily polluted by chlor-alkali industrial activity. The seasonal variations of the Hg dynamics in the aquatic environment were assessed using total Hg concentrations in bottom sediment and suspended matter, and total and reactive dissolved Hg concentrations in the water. The impact of the chlor-alkali plant (CAP) remains the largest concern for Hg contamination of this river system. Upstream from the CAP, the Hg partitioning between dissolved and particulate phases was principally controlled by the dissolved fraction due to snow melting during spring high flow, while during low flow, Hg was primarily adsorbed onto particulates. Downstream from the CAP, the Hg partitioning is controlled by the concentration of dissolved organic and inorganic ligands and by the total suspended sediment (TSS) concentrations. Nevertheless, the particulate fluxes were five times higher than the dissolved ones. Most of the total annual flux of Hg supplied by the CAP to the river is transported to the outlet of the catchment (total Hg flux: 70 μg m⁻² a⁻¹). Downstream from the CAP, the bottom sediment, mainly composed of coarse sediment (>63 μm) and depleted in organic matter, has a weak capacity to trap Hg in the river channel and the stock of Hg is low (4 mg m⁻²) showing that the residence time of Hg in this river is short.     

The nature and distribution of Cu,Zn, Hg,and Pb in urban soils of a regional city: Lithgow,Australia

This study investigates the concentration and spatial distribution of Cu, Zn, Hg and Pb in the surface (0–2 cm) soils of a regional city in Australia. Surface soils were collected from road sides and analysed for their total Cu, Zn, Hg and Pb concentrations in the <180 μm and <2 mm grain size fractions. The average metal concentration of surface soils, relative to local background soils at 40–50 cm depth, are twice as enriched in Hg, more than three times enriched in Cu and Zn, and nearly six times as enriched in Pb. Median surface soil metal concentration values were Cu – 39 mg/kg (682 mg/kg max), Zn – 120 mg/kg (4950 mg/kg max), Hg – 44 μg/kg (14,900 μg/kg max) and Pb – 46 mg/kg (3490 mg/kg max). Five sites exceeded the Australian NEPC (1999) 300 mg/kg guideline for Pb in residential soils. Strong positive correlations between Cu, Zn and Pb, coupled with the spatial distribution of elevated soil concentrations towards the city centre and main roads suggest traffic and older housing as major sources of contamination. No spatial relationships were identified between elevated metal loadings and locations of past or present industries.     

Human Health Risk Assessment of a landfill based on volatile organic compounds emission,immission and soil gas concentration measurements

A Human Health Risk Assessment (HHRA) was required for a closed landfill located in Cerdanyola del Vallès (Barcelona, Spain). The HHRA had two objectives, to evaluate the present risk of the identified receptors in the area and to safely develop the future urban planning of the area, therefore 3 scenarios for the current situation and 4 for the future situation were developed.After reviewing the existing data and exploring the needs of information, the assessment in this study was focused on the measurement of volatile organic compounds (VOCs) fluxes from the subsoil (emission from the landfill at 5 points), concentrations of VOCs in the air (immission in 4 urban sites) and concentration of VOCs in soil–gas (measurements at 5 m below ground surface outside the landfill at 8 sites). Around 70 VOCs were analyzed by using multi-sorbent tubes and Thermal Desorption Gas Chromatography (TD–GC–MS). The VOCs that were detected and quantified include alkanes, aromatic hydrocarbons, alcohols, ketones, halocarbons, aldehydes, esters, terpenoids, ethers and some nitrogenated and sulfur compounds, furans and carboxylic acids. Specific mercury flux measurements were performed in a hot spot by using carulite tubes, that were also analyzed by using Thermal Decomposition, Amalgamation, and Atomic Absorption Spectrophotometry.Results showed average values of volatile emission fluxes ranging from non-detected to 331 μg m⁻² day⁻¹ (dichlorodifluoromethane). In the case of immission, the concentration of VOCs measured in the air of populated area surrounding the landfill ranged values from non-detected to 42.0 μg m⁻³ (acetic acid). The soil–gas measurements in piezometers around the landfill showed individual VOC values with a maximum 830 μg m⁻³ for dichlorodifluoromethane.With the obtained fluxes and concentrations in air and soil–gas, USEPA methodology and modeling was used to evaluate equivalent concentration in the scenarios considered. Toxicity values from IRIS database were used to finally obtain chemical risk indicators. Admissible risk indicators were obtained in all scenarios. The VOCs that contributed more to risk indexes in RH2 were trichloroethylene, trimethylbenzene, chloroform, 1,2-dichloroethane and carbon tetrachloride. The carcinogenic risk in RH7 was linked to the presence of benzene and chloroform. The comparison of the measurements of the present work with other landfills evidence that HHRA in ambient air would be needed in order to perform a correct landfill management.     

Levels of selected potential harmful elements (PHEs) in soils and vegetables used in diet of the population living in the surroundings of the Estarreja Chemical Complex (Portugal)

This study was carried out to analyze the distribution and soil–plant transfer of selected potential harmful elements (PHEs: As, Hg and Zn) in soils and in two edible horticultural crops (cabbage, Brassica oleracea L., and tomato, Lycopersicon esculentum Mill). randomly sampled in kitchen gardens/small farms around one of the most important and old Portuguese industrial areas (Estarreja Chemical Complex-ECC). The results show that 46% and 11.5% of the soils present high total As (12–532 mg/kg) and Hg (6.6–13.65 mg/kg) concentrations that exceed protective health Canadian soil quality guidelines. Soil As and Zn available fractions are also of concern for groundwater and crops contamination as more than 84% of the samples were above the trigger value proposed by the German legislation for both elements (0.4 and 2 mg/kg, respectively). In the horticultural crops the cabbage leaves concentrate more the PHEs (max.: 3.5, 0.08 and 746 mg/kg dw for As, Hg and Zn, respectively) than the tomato fruit (max.: 0.4, 0.02 and 82 mg/kg dw, respectively). The highest concentration of the study PHEs in soils and horticultural crops were found near sewage outlets that are chiefly related to historical industrial activities mostly from arsenopyrite roasting and a chloralkali plant. The values of estimated bioaccumulation and bioconcentration coefficients suggested exclusion mechanisms for transfer of As to edible cabbage and tomato tissues and cabbage Zn tolerance capacity. The concentration of the PHEs in the edible horticultural crops tissues were not directly related with respective soil total concentration or available fractions, specially for As and Hg. Sampling locations with the highest concentrations of As, Hg, Zn in soil and vegetable foodstuffs should be sites to foregoing research and human daily intakes should be investigated in order to evaluate potential health risks.     

Metal mobility by de-icing salt from an infiltration trench for highway runoff

Soil from an infiltration trench for highway runoff was leached in columns alternately with NaCl and de-ionised water to simulate the runoff of de-icing salt into the trench followed by snowmelt or rainwater. Simultaneously, two columns with the same soil were leached with de-ionised water throughout the experiment. In addition, the groundwater below the infiltration trench was sampled on some occasions. The column leachate and groundwater were split into two sub samples, one was filtered though a 0.45 μm filter; both were analysed for Pb, Cd, Zn, Fe and total organic carbon (TOC). The column experiment showed clearly that an extensive mobilisation of Pb occurred in low electrolyte water leaching following NaCl leaching. The high Pb concentration coincided with peaks in Fe and TOC concentrations and implied colloid-assisted transport. Conversely, Cd and Zn concentrations were raised in the NaCl leachate and a high correlation with Cl showed that Cl complexes are important for the mobilisation, although a pH effect and ionic exchange cannot be excluded. Only 0.15% and 0.06% of the total amount of Pb was leached from the columns leached with alternating NaCl and deionised water confirming the usual hypotheses about the high immobility of Pb in soils. However, on one occasion when the ionic strength and pH was the lowest measured the concentration of Pb in groundwater sampled from 2.5 m depth was 27 μg L⁻¹ in the dissolved phase (<0.45 μm) and 77 μg L⁻¹ in the particle phase (>0.45 μm). These Pb concentrations are almost 3 and 8 times above the Swedish limit for drinking water quality. Accordingly, in spite of the immobility of Pb the accumulation in roadside soils is so large that groundwater quality is threatened. In conclusion, the study suggests that roadside soils impacted by NaCl from de-icing operations contribute Pb to groundwater by colloid-assisted transport.     

Laboratory study of calcite–gypsum sludge–water interactions in a flooded tailings impoundment at the Kristineberg Zn–Cu mine,northern Sweden

Due to liming of acid mine drainage, a calcite–gypsum sludge with high concentrations of Zn (24,400 ± 6900 μg g⁻¹), Cu (2840 ± 680 μg g⁻¹) and Cd (59 ± 20 μg g⁻¹) has formed in a flooded tailings impoundment at the Kristineberg mine site. The potential metal release from the sludge during resuspension events and in a long-term perspective was investigated by performing a shake flask test and sequential extraction of the sludge. The sequentially extracted carbonate and oxide fractions together contained ⩾97% of the total amount of Cd, Co, Cu, Ni, Pb and Zn in the sludge. The association of these metals with carbonates and oxides appears to result from sorption and/or coprecipitation reactions at the surfaces of calcite and Fe, Al and Mn oxyhydroxides forming in the impoundment. If stream water is diverted into the flooded impoundment, dissolution of calcite, gypsum and presumably also Al oxyhydroxides can be expected during resuspension events. In the shake flask test (performed at a pH of 7–9), remobilisation of Zn, Cu, Cd and Co from the sludge resulted in dissolved concentrations of these metals that were significantly lower than those predicted to result from dissolution of the carbonate fraction of the sludge. This may suggest that cationic Zn, Cu, Cd and Co remobilised from dissolving calcite, gypsum and Al oxyhydroxides were readsorbed onto Fe oxyhydroxides remaining stable under oxic conditions. In a long-term perspective (≳10² a), ⩾97% of the Cd, Co, Cu, Ni, Pb and Zn content of the sludge potentially is available for release by dissolution of calcite and reductive dissolution of Fe oxyhydroxides if the sludge is subject to a soil environment with lower dissolved Ca concentrations, pH and redox than in the impoundment.     

Mercury in the Lot–Garonne River system (France): Sources,fluxes and anthropogenic component

Dissolved and particulate Hg fluxes in the Lot–Garonne–Gironde fluvial-estuarine system were obtained from observation of daily discharge and suspended particulate matter (SPM) concentrations. In addition to the measurements of the total dissolved (<0.45 μm) and particulate Hg (>0.45 μm), called HgT_D and HgT_P respectively, the dissolved inorganic Hg species (HgR_D) were determined monthly. Geochemical background values for HgT_P in sediments and SPM were similar to crustal values and to typical concentrations in SPM of non-contaminated river systems, respectively. The Riou Mort watershed already known as the origin of important historical polymetallic (e.g., Cd, Zn) pollution was identified as an important Hg point source. In the downstream Lot River, Hg concentrations were clearly higher than those in other moderately contaminated systems. The mean relative contribution of HgR_D to HgT_D in the Lot River and in the Garonne River was close to 25% and 50%, respectively, and showed no correlation with water discharge or SPM concentration. Depending on the origin and nature of SPM, HgT_P concentrations were correlated or not with particulate organic C (POC). Maximum HgT_P concentrations were measured in samples containing low POC concentrations and were attributed to sediment resuspension. In contrast, high POC concentrations (6–17%) during algal blooms were associated with low/moderate HgT_P concentrations (<0.5 mg kg⁻¹) at different sites, suggesting that Hg concentrations in fluvial phytoplankton may be limited by bioavailability of dissolved Hg and/or physiologically controlled Hg accumulation. Mercury was mostly (up to 98%) transported in the particulate phase with estimated annual Hg fluxes at the outlet of the Lot River system ranging from 35 to 530 kg a⁻¹ for the past decade. The minimum anthropogenic component (58–84% of total Hg fluxes) could not be explained by present Riou Mort point source contributions, suggesting important Hg release from contaminated sediment as a major source and from downstream point sources (e.g., coal-fired power plants and/or metal processing industries). HgT_P concentrations and fluxes were strongly related to hydrologic variations and were clearly increased by riverbed dredging during lock construction. Therefore, the estimated Hg stocks in the Lot River sediment (5–13 tons) represent an important potential Hg source for the downstream fluvial-estuarine system.     

Elemental sulfur in drain sediments associated with acid sulfate soils

This paper reports the abundance of elemental S in drain sediments associated with acid sulfate soils. The sediments exhibited near-neutral pH (5.97–7.27), high concentrations of pore-water Fe²⁺ (1.37–15.9 mM) and abundant oxalate-extractable Fe (up to 4300 μmol g⁻¹). Maximum acid-volatile sulfide (AVS) concentrations in each sediment profile were high (118–1019 μmol g⁻¹), with AVS often exceeding pyrite-S. Elemental S occurred at concentrations of 13–396 μmol g⁻¹, with the higher concentrations exceeding previous concentrations reported for other sedimentary systems. Up to 62% of reduced inorganic S near the sediment/water interface was present as elemental S, due to reaction between AVS and oxidants such as O₂ and Fe(III). Significant correlation (r = 0.74; P < 0.05) between elemental S and oxalate-extractable Fe(III) is indicative of elemental S formation by in situ oxidation of AVS. The results indicate that AVS oxidation in near-surface sediments is dynamic in acidified coastal floodplain drains, causing elemental S to be a quantitatively important intermediate S fraction. Transformations of elemental S may therefore strongly influence water quality in ASS landscapes.     

Dissolved and particulate zinc and nickel in the Yangtze River (China): Distribution,sources and fluxes

Dissolved and particulate Zn and Ni concentrations were determined at 76 locations along the Yangtze River basin from the headwaters to the estuary during flood and dry seasons. Spatial and temporal variations of Zn and Ni were investigated and six major source zones were identified. The Three Gorges Dam (TGD) blocked most of the suspended loads and extremely low concentration of Zn and Ni were observed downstream of the dam. Dissolved (ranging from 0.062 to 8.0 μg L⁻¹) and particulate (ranging from 12 to 110 mg kg⁻¹) Ni showed similar levels of concentrations during flood and dry seasons, whereas dissolved (ranging from 0.43 to 49 μg L⁻¹) and particulate (ranging from 54 to 1100 mg kg⁻¹) Zn were slightly and much lower in the flood season than dry season, respectively. This was attributed to the increased water discharge during the flood season causing a dilution effect and sediment resuspension. In the flood season, average concentrations of Zn and Ni were higher in the main channel than in tributaries, due to soil erosion and mining activities providing the dominant inputs. The situation was opposite in the dry season, attributed to the contribution of municipal sewage, industrial activities, and waste disposal. During the flood season, dissolved Zn and Ni concentrations were negatively correlated with pH. Water and suspended particulate matter (SPM) from the upper reaches, middle reaches, and lower reaches of the Yangtze River were characterized by their Zn and Ni concentrations. The Panzhihua, Nanling and Tongling mining areas were considered as the most important source zones of particulate Zn and Ni. The Chongqing region, Wuhan region and the Yangtze River Delta provided most of the dissolved Zn and Ni inputs into the river. Annual net flux of Zn (10–72 × 10⁵ kg a⁻¹) and Ni (5.0–19 × 10⁵ kg a⁻¹) in each source zone were estimated according to their respective influent and effluent fluxes. Contributions of the source zones to Zn and Ni transport decreased from the upper reaches to the lower reaches.     

Arsenic immobilization in water and soil using acid mine drainage sludge

Adsorption onto Fe-containing minerals is a well-known remediation method for As-contaminated water and soil. In this study, the use of acid mine drainage sludge (AMDS) to adsorb As was investigated. AMDS is composed of amorphous particles and so has a large surface area (251.2 m² g⁻¹). Here, adsorption of both arsenite and arsenate was found to be almost 100%, under various initial AMDS dosages, with the arsenate adsorption rate being faster. The optimum pH for As adsorption onto AMDS was pH 7.0 and the maximum adsorption capacities for arsenite and arsenate were 58.5 mg g⁻¹ and 19.7 mg g⁻¹ AMDS, respectively. In addition, experiments revealed that AMDS dosages decreased As release from contaminated soil. Therefore, the AMDS used in this study was confirmed to be a suitable candidate for immobilizing both arsenite and arsenate in contaminated soils.